4. Getting rid of your outdated fan
Price: $75-$300 depending on how fancy or effective you need it to be. (Pro tip: you can often find a worthwhile fan in a junkyard if you do your research and know what will fit your car.)
If your car is from the '90s or earlier, your cooling fan isn't terribly efficient. It's driven by the engine, so it robs power, even when it's not needed -- something known as "parasitic power loss." It operates using a clutch that tends to wear out over time, at which point your fan's cooling ability fades dramatically. Switching to an electric fan gets back the horsepower that's otherwise lost, and keeps the fan running as long as you need to keep temperatures in check, even if your car is off.
If your car is more modern, this likely won't apply to you. It's more of an old hot rodder's trick that the manufacturers eventually adopted.